The present invention generally relates to vehicle steering systems suitable for use with off-road, amphibious, and water vehicles that are propelled by two or more propulsion devices, such as drive wheels, drive tracks, propellers, etc. More particularly, the present invention relates to a vehicle steering control system that utilizes two synchronized steering input levers in a steer-by-driving propulsion system.
Ride-on self-propelled lawn care equipment, such as fertilizer and herbicide spreaders, are known and commercially available. A notable example is the Permagreen Ride-On Magnum, available from Permagreen Supreme Inc. and depicted in FIG. 1. As evident from FIG. 1, the Permagreen Ride-On Magnum utilizes an articulated steering system in which turning of the vehicle 10 occurs as a result of its front end 12 (with drive wheels 14) being physically turned with the handle bar 16, causing the motorized front end 12 to articulate relative to a trailing sulky 18. Articulated steering systems of this type usually depend entirely on an operator's muscle power to steer the vehicle. For example, U.S. Pat. No. 6,336,600 to Jessen discloses a self-propelled fertilizer spreader vehicle with an articulated steering control system, in which a front section of the vehicle is pivotally connected to a rear section and steered by changing the angle of the pivotal connection.
Aside from systems that control the steering angle of steering wheels (for example, conventional automobile steering systems), another type of steering system widely found in lawn care equipment is the steer-by-driving (drive-wheel steering) system. Also widely used on a variety of off-road and amphibious vehicles, steer-by-driving systems operate by controlling the relative rotation speed of at least two drive means (wheels, tracks, or other propulsion devices) to cause the vehicle to turn to the side of the slower rotating drive means. Such steer-by-driving systems are well known in the art, and include, but are not limited to, controlled differential steering, clutch-brake steering, and independent wheel-motor steering units. Controlled differential steering units generally comprise a differential that operably connects lefthand and righthand drive wheels or tracks and selectively-operable brakes that retard the rotation of one of the drive means. Examples include bulldozers and multi-wheeled vehicles such as skid steer loaders. In clutch-brake steering units, lefthand and righthand drive wheels are operably connected by selectively operable clutches with or without brakes for retarding the rotation of one of the drive wheels. A common example of this type of steering unit can be found in commercial lawn mowers and the like. Finally, in independent wheel-motor steering, each drive wheel is operably mounted directly to an electric or hydraulically driven wheel-motor or variable-displacement hydrostatic transmission that can be selectively-controlled to retard the rotation of either drive wheel. A common example of this type of steering unit is the zero-turning radius lawn mowers and the like.
U.S. Pat. No. 5,913,802 to Mullet et al. discloses a tiller or single-lever steering device for a drive-wheel steering system on a zero-turn-radius lawn mower. Single-lever steering devices, for example, the handlebars of tricycles and bicycles, are widely used and enable the user to become quickly proficient at operating other vehicles with single-lever steering. Both hands can remain on the lever (handlebar) for support, or one hand may be removed while the other hand still provides full steering control. Another advantage of single-lever steering devices is their compact size, which can minimize the overall size of the vehicle. Single-lever steering devices are also common on personal watercraft, personal recreational vehicles such as ATVs, amphibious vehicles, lawn and garden vehicles, and the like. In addition to drive-wheel steering systems such as Mullet et al., single-lever steering systems can be connected to a variety of other vehicle steering systems, including linkage-steering and direct-steering (for example, bicycles) systems.
While having the above-noted advantages, single-lever steering devices have known shortcomings. For example, the tiller motion of the lever mayforce the operator's body out of optimal alignment with the vehicle, such as when making a sharp high-speed turn, in which case the operator's body should lean to the inside of the turn for balance while the tiller must be orientated to the outside of the turn. Furthermore, vertically-orientated steering shafts common to single-lever steering devices may restrict entry to the vehicle and interfere with the placement of other vehicle components. Without some form of power-assist, the forces required to move the lever can fatigue the operator and often limit the size of the vehicle that can be controlled with a single-lever steering device.
Two-lever steering devices are also known. Conventional two-lever steering devices use two independently operable levers, normally arranged side by side, which move fore and aft in relationship to the vehicle. Conventional two-lever steering systems are commonly used to control differential steering systems, clutch-brake steering systems, steering systems utilizing twin independent variable-displacement hydraulic pumps and fixed-displacement hydraulic wheel motors, and twin variable-displacement hydrostatic transmission steering systems. Two-lever steering devices are commonly used with drive-wheel steering control systems found on walk-behind, sit-on, stand-on, skid steer, and stand-on/walk-behind vehicles.
Conventional two-lever steering input device systems also have known shortcomings. When used on walk-behind, stand-on, and stand-on/walk-behind vehicles as disclosed in U.S. Pat. No. 6,490,849 to Scag and U.S. Pat. No. 6,912,831 to Velke, a fixed support bar must be provided so the operator can maintain a firm grip on the vehicle. However, the operator is often required to loosen his/her grip on the fixed support bar while operating the steering levers, which can compromise operator stability and safety. Two-lever steering has been adapted to control differential steering systems used extensively in tracked vehicles, such as bulldozers and tanks, to provide an easy way to steer a heavy vehicle by braking the track on one side of the vehicle while the power is transmitted through a differential to continue turning the track on the other side at a higher speed. Typically, independently operable right and left handles control the brakes. While controlled differential steering systems perform well when the operator is sitting, in the case of a stand-up operator position such as on ride-on self-propelled lawn care equipment, additional structure is necessary to provide the operator with stable support. For example, a fixed support bar may be necessary so that the operator can maintain a firm grip on the vehicle for both vehicle control and operator stability and safety over rough and hilly terrain. Even then, the constant use of the fingers to operate the steering levers can cause fatigue and strain on the hands and arms, and accelerations and decelerations can cause the operator's arms on the steering levers to apply a reverse input to the steering system. A one-hand steering capability to free one hand of the operator is not practical unless the two levers are closely orientated to permit one hand to operate both levers. However, close placement of both levers may restrict entry onto the vehicle or in otherwise interfere with the operator or the location of other components, necessitating the use of burdensome and complicated means to reposition the levers as disclosed in U.S. Pat. Nos. 7,299,610 to Piontek and 6,729,115 to Bartel. Lastly, conventional two-lever steering input devices are less instinctive to use, requiring a lengthy learning curve before an inexperienced operator becomes proficient in its operation.
Another example of a two-lever steering device is disclosed in U.S. Pat. No. 6,604,757 to Huang as installed in a conventional automobile steering wheel system. Two counter-operating steering levers are connected to a linkage steering system to adjust the steering angle of the front wheels of a beach motorized vehicle. A more complicated two-lever steering device for a conventional steering wheel system is disclosed in U.S. Pat. No. 6,827,174 to Chernoff et al. In Chernoff et al., right and left control posts (levers) mechanically communicate with each other so as to operate in opposite directions by means of gears, etc. The posts send non-mechanical steering signals to a steer-by-wire system to adjust the steering angle of the steering wheels of a vehicle. Chernoff et al. also disclose separate demand-input mechanisms on the posts to control other vehicle control systems, for example, nonmechanical accelerator and braking signals. Unfortunately, steer-by-wire systems require expensive and complicated electronic control systems, as well as expensive and complicated actuators to transform the electrical signals into mechanical motion capable of operating the steering device. As such, steer-by-wire systems tend to be impractical for use on anything less than mass production vehicles.